Using the 'IBM 5081 12' monitor with VGA cards
----------------------------------------------

This 19" monitor was originally used with the IBM 5080 workstation,
and has RGB inputs and outputs.  Sync is to be provided on the Green
signal.

There are some conversion guides on Internet that attempt to add sync
to the Green signal in an external box, but I decided it would be more
convenient to just modify the monitor to accept separate H and V sync
signals instead of the sync-on-green.  No external box necessary, and
less chance of disturbing the high-bandwith video signal by adding
extra circuitry.

The required circuit is very simple: just combine the separate H and V
sync signals, do a level conversion to 12v, and feed it into the
original sync-separator circuit using a convenient test jumper.


                                           +--|=====|----O +12V
                         +-----+           |    2k2
   HSync  O--------------|     |       |---+-------------O Sync out
                         |  +  |o------|
   VSync  O--------------|     |       |---+
                         +-----+     BS170 |
                         74LS02           ---

Additionally, a standard 5V regulator is required to supply the 74LS02:

                         +-----+
                         |     |
   +12V   O-------+------|     |-----------+-------------O +5V
                  |+     |     |           |+
                 ===     +-----+ 78L05    ===
                  | 10u T   |              | 10u T
                 ---       ---            ---

These components can be fitted on a small prototype board, including
two RCA (female) plugs for the HSync and Vsync signals, and a thick
(2mm) pin for the Sync out signal.  +12V is supplied via a wire.

This small board can be attached to the cable connected to the "A"
board (the board containing the video amps attached to the metal box
at the rear of the unit), using a tywrap.

Connections are made as follows:

- the cables from the Red and Greed "video OUT" BNCs are detached from
  the video splitter/amp boxes mounted on the bottom of the unit, and
  connected to the HSync and VSync RCA input plugs of the circuit.

- the green flying wire on the "A" board, which is a test jumper for the
  sync separator, is disconnected from the "A" board and connected to
  the "Sync out" pin of the added circuit board.

- +12V is connected to TP403 on the "A" board (at the board edge close
  to the picture tube neck)


Now, the monitor can be connected to a VGA card using a standard VGA-BNC
cable.  The Red and Green Video out BNCs are used for Sync, it does not
matter which is used as Hsync or Vsync.

Of course, the card must output a 64 KHz Horizontal and 60 Hz Vertical
signal!  I don't know how Windows could be made to do that, but on my
Linux system with XFree86 I use the following modelines:

    ModeLine "1152x908"   97.82 1152 1244 1344 1528  908  978  994 1067
    ModeLine "1280x1024" 110.11 1280 1388 1488 1720 1024 1030 1046 1067

Note that you will have to re-align the entire picture geometry and
convergence to switch between the two modes shown above.  1280x1024 is
the normal operation mode, but I use the smaller resolution to get a
bit easier readable characters.
See http://www.devo.com/video for some alignment information.  It is
about a later version of the monitor, but much of it still applies.

When the picture is square (not using the entire display width), and
cannot be made to fit using the display width setting, find the two
green jumper wires near the top of the "D" board and switch them from
the "N" to the "W" position.

Of course all of the above should be attempted only by persons with some
experience in building electronic circuits.  Be careful, dangerous
voltages are present in the monitor at many places!

Rob PE1CHL